This invention relates generally to gas cluster ion beam (GCIB) processing equipment, and, more particularly to incorporating means within GCIB processing equipment for eliminating monomer ions from the ion cluster beam without the production of unwanted heat.
The use of gas cluster ion beams for etching, cleaning, and smoothing of material surfaces is known in the art(see for example Deguchi et al., U.S. Pat. No. 5,814,194). For purposes of better understanding the present invention, gas clusters are nano-sized aggregates of materials that are gaseous under conditions of standard temperature and pressure. Such clusters typically consist of aggregates ofxcx9cseveral tens toxcx9cseveral thousand atoms or molecules loosely bound to form the cluster. Such clusters can be ionized by electron bombardment or other means, permitting them to be formed into directed beams of known and controllable energy. The larger sized clusters are the most useful because of their ability to carry substantial energy per cluster ion, while having modest energy per atom or molecule. The clusters disintegrate on impact, with each individual atom or molecule carrying only a small fraction of the total cluster energy. Consequently the impact effects of large clusters are substantial, but are limited to a very shallow surface region. This makes ion clusters effective for a variety of surface modification processes, without the tendency to produce deeper subsurface damage characteristic of monomer ion beam processing.
Means for creation of and acceleration of such GCIB are described in the reference previously cited. Presently available ion cluster sources produce clusters ions having a wide distribution of sizes, N (where N=the number atoms or molecules in each cluster).
Because monomer ions as well as cluster ions are produced by presently available cluster ion beam sources, those monomer ions are accelerated and transported to the workpiece being processed along with the cluster ions. Upon acceleration in an electric field, monomers, having low mass, obtain high velocities that allow the light monomers to penetrate the surface of the workpiece and produce deep damage which is likely to be detrimental to the intended process. Such sub-surface ion damage is well-established and well-known from the more traditional monomer ion beam processing art and can produce a wide variety of deep damage and implantation.
It is also known in the ion cluster beam art that many GCIB processes benefit from incorporating means within GCIB processing equipment for eliminating monomer ions from the ion cluster beams. Electrostatic and electromagnetic mass analyzers have been employed to remove light ions from the beam of heavier clusters (see Knauer, U.S. Pat. No. 4,737,637 and Aoyanagi et al. in Japanese laid open application JP 03-245523A1 corresponding to Japanese application JP 2-43090, cited as prior art in Aoyagi et al., U.S. Pat. No. 5,185,287). Electrostatic and electromagnetic mass analyzers have also been employed to select ion clusters having a narrow range of ion masses from a beam containing a wider distribution of masses (see Knauer, U.S. Pat. No. 4,737,637 and Aoki, Japanese laid open application JP 62-112777A1).
In the past, electromagnetic beam filters have been used to separate ion masses. However, electromagnets are costly and, while in use, continually consume electrical power. Furthermore, the electrical power is converted to heat. Since the magnetic beam filter must be deployed in a vacuum chamber, namely the ionization/acceleration chamber, convection cooling of the beam filter is not practical. Generally, conductive paths to water or other fluid cooling systems must be provided and heat exchangers are required to remove heat from the cooling fluid and transfer it to the environment. Such cooling apparatus adds additional cost and introduces maintenance problems. The use of an electromagnetic beam filter is undesirable for these and other reasons.
It is therefore an object of this invention to reduce the heat produced in GCIB processing equipment and to eliminate the need for water or other cooling of a beam filter device.
It is a further object of this invention to separate undesired monomer ions from the GCIB.
It is still a further object of this invention to reduce the cost, weight, and maintenance complexity of a GCIB processing system
The objects set forth above as well as further and other objects and advantages of the present invention are achieved by the embodiments of the invention described hereinbelow.
The present invention is capable of reducing the heat produced in GCIB processing equipment, thus eliminating the need for water or other cooling of a beam filter device utilized therein. The invention utilizes a permanent magnet beam filter or a hybrid permanent electromagnetic beam filter to separate undesired monomer ions from the GCIB. Consequently the present invention substantially reduces the cost, weight, and maintenance complexity of a GCIB processing system over GCIB systems which incorporate a conventional electromagnetic beam filter system therein.